The GHK 551 conversion kit for the GHK 553 is designed to work with both versions (standard and QPQ) of the GHK 553. This will in turn change your short barreled 553 into a carbine length 551.
The GHK 551 conversion kit for the GHK 553 is designed to work with both versions (standard and QPQ) of the GHK 553. This will in turn change your short barreled 553 into a carbine length 551.